JP3264370B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor device and, more particularly, to a structure for reducing a load capacitance of a source follower amplifier.

[0002]

2. Description of the Related Art Conventionally, in semiconductor devices, a source follower is often provided on-chip for impedance conversion when an output is taken out to an external circuit. The load capacitance of the on-chip source follower amplifier is the wiring capacitance,
It is formed by the sum of the junction capacitance of the output diffusion layer, the input capacitance of the external circuit at the next stage of the on-chip source follower amplifier, and the capacitance of the protection circuit at the source follower output terminal. Assuming that the transconductance of the drive-side transistor is gm and the load capacitance is C, the band of the source follower is represented by gm / C.
Needs to be smaller.

In Japanese Patent Application Laid-Open No. 61-005680, a bipolar driver transistor 141, which is usually formed as an external circuit in the next stage of an on-chip source follower amplifier, is formed on-chip, and the wiring capacitance and input capacitance are reduced by shortening the wiring. (See FIG. 5). 5, reference numeral 106 denotes a package, 141 denotes a transistor single chip, 107 denotes an image sensor chip, and 103 denotes a CCD.
Group, 104 is an amplifier, 143, 143 'are leads, 1
23 'and 142 are terminals, 124' is a pin terminal, 125 is an external wiring, 109 is a parasitic capacitance, 126 is a pull-down resistor, and 110 is a signal processing unit.

In Japanese Patent Application Laid-Open No. 63-199507, gm of a source follower is increased by applying a push-pull operation by inputting an inverted pulse of a driver transistor input pulse to a load transistor gate of a source follower (see FIG. 6). In FIG.
Is a positive power supply line, 202 is a negative power supply line, 203 is an input terminal, 204 is an output terminal, B1 and B2 are bias points, CL
Is the load capacity.

[0005]

However, the conventional method does not sufficiently reduce the load capacity. Also, as in Japanese Patent Application Laid-Open No. 61-005680, it is troublesome to form and bond a source follower amplifier in a MOS process and a transistor in a bipolar process as separate chips in separate processes. Also, JP-A-63-199507
In the publication, at least one extra inverter is required.

[0006]

According to a first aspect of the present invention, there is provided a semiconductor device in which a connection terminal including an output terminal of a semiconductor device is mounted to electrically connect to an external device. A circuit element is electrically connected to the output terminal when the semiconductor device is not mounted,
When the semiconductor device is mounted, it is electrically disconnected from the output terminal.

According to a second semiconductor device of the present invention, there is provided a semiconductor device in which a semiconductor device is packaged and a connection terminal including an output terminal of the package is mounted to make an electrical connection with the outside. A circuit element is connected between an output terminal of the package and a reference potential;
The output terminal and the protection circuit element are electrically connected when the package is not mounted, and are electrically disconnected when the package is mounted. is there.

In a third semiconductor device according to the present invention, a protection circuit element is provided between an output terminal of a packaged semiconductor device and a reference potential terminal, and one end of the protection circuit element is electrically connected to the reference potential terminal. The other end of the protection circuit element is electrically connected to the output terminal when the semiconductor device is removed from the socket,
When the semiconductor device is inserted into a socket, the semiconductor device is not electrically connected to the output terminal.

In a fourth semiconductor device according to the present invention, in the third semiconductor device, the protection circuit element is embedded in the back surface of the package, and a portion of the back surface of the package in which the protection circuit element is embedded is concave. It is characterized by having.

According to a fifth aspect of the present invention, there is provided a semiconductor device comprising:
4. The semiconductor device according to claim 4, wherein an output circuit of the semiconductor device is an on-chip source follower amplifier.

A sixth semiconductor device according to the present invention is characterized in that
5. The semiconductor device according to any one of items 5, wherein the semiconductor device is a solid-state imaging device.

(Operation) The protection circuit mainly applies a high voltage erroneously when a bias is applied to a device, or a high voltage is applied by static electricity of a human or the like at the time of bonding when assembling the device into a package. This prevents the diffusion layer from being destroyed by applying a high voltage due to static electricity when a human touches a device assembled in the package.

A protection circuit is also required for the output diffusion layer, but if a protection circuit is provided, the output wiring must be connected to the diffusion layer of the protection circuit. Will be added. Fortunately, the output wiring is not biased externally,
When a bias is applied to the device when using the above-described device, a high voltage is not erroneously applied and the diffusion layer is not destroyed. In the output diffusion layer, the protection circuit is not necessary when the device is operating, but is necessary only when there is a possibility that the device is destroyed by static electricity caused by a person or the like.

Therefore, in the present invention, a protection circuit element is connected when the device is detached from the apparatus, and is not connected when the device is mounted on the apparatus, so that a load capacity does not occur during operation.

[0015]

FIG. 1 shows an embodiment of the present invention. FIG. 1A is a perspective view when the device is removed from the apparatus, and FIG. 1B is a perspective view when the device is mounted on the apparatus. FIG. 1C is an enlarged view of a contact portion between the output terminal 4 and the terminal of the protection circuit element 3.

A semiconductor device 2 as a semiconductor device is mounted in a package 1. In the semiconductor device 2, a source follower is often provided on-chip for impedance conversion when an output is taken out to an external circuit.

FIG. 3 shows a source follower amplifier. A gate oxide film, a gate electrode 9, and an N ⁺ diffusion layer 8 are formed on the P-type region 7.
And a driver transistor 16 and a load transistor 17 are formed. Voltage VDD 10 is applied to the drain of driver transistor 16, a signal is applied to input terminal 12 connected to gate electrode 9, and a signal is output from output terminal 13 connected to the source.
The gate and source of the load transistor 17 are ground 1
1 and the drain is shared with the source of the driver transistor 16, and a signal is output from the output terminal 13. The channel of the load transistor 17 is doped with an N-type impurity to form an N-type region 14.

In order to prevent the breakdown of the diffusion layer and the lower layer due to static electricity or the like, for example, V
A transistor-type protection circuit as shown in FIG. 4 is provided which breaks down when a required voltage plus a voltage of alpha is applied to DD10. This transistor has a characteristic that the threshold voltage is positive and cut off when the threshold voltage is lower than the threshold voltage. Therefore, when the gate and the source are connected to the ground 11 and the drain is connected to the VDD 10 as shown in FIG. 4, the power supply voltage VDD is positive, so that it is normally cut off. If the voltage required for VDD plus the voltage of alpha is applied to the drain of this transistor so that breakdown occurs, no excessive voltage is applied to the VDD diffusion layer, and the circuit of FIG. 4 functions as a protection circuit. .
On the other hand, the output terminal 13 is also connected to the output layer (the driver transistor 1).
(Source No. 6) is connected, so that a protection circuit is required to prevent breakdown of the output diffusion layer due to static electricity or the like. However, in the output layer, the capacity of the protection circuit becomes the load capacity of the source follower amplifier at the time of actual signal output.

Therefore, in the present invention, the output terminal 4 of the package of the on-chip source follower amplifier and the ground terminal (the reference potential terminal. The reference potential may be a fixed potential, not necessarily the ground) 5. The protection circuit element 3 (for example, a Zener diode) having a withstand voltage and a required voltage plus alpha is connected therebetween. However,
The terminal connected to the output terminal 4 should not be in electrical contact with the foot of the package when the package is inserted into the socket. In FIG. 1, the protection circuit element 3
The ends of the wire are ring-shaped, the protection circuit element 3 and the ground terminal 5 are connected, and the protection circuit element 3 and the output terminal 4 are insulated. Further, an insulating portion 6 is provided above the output terminal 4.
In addition, if the output terminal 4 and the terminal of the protection circuit element 3 are normally in electrical contact with each other so that the wire of the protection circuit element 3 has elasticity, and the package 1 is inserted into the socket, When the protection circuit element 3 is pressed, the protection circuit element 3
The terminal goes to the insulating portion 6 of the output terminal 4 so that the output terminal 4 and the terminal of the protection circuit element 3 are not in electrical contact.

When the package 1 is removed from the socket, the output terminal 4 and the terminal of the protection circuit element 3 make electrical contact again because the wire of the protection circuit element 3 has elasticity.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

A first embodiment of the present invention will be described with reference to FIG. As described above, FIG. 1A is a perspective view when the device is removed from the apparatus, and FIG. 1B is a perspective view when the device is mounted on the apparatus. FIG. 1C is an enlarged view of a contact portion between the output terminal 4 and the terminal of the protection circuit element 3.

Here, the semiconductor element 2 is a solid-state image sensor, and the solid-state image sensor is mounted in the package 1.
Generally, in a solid-state imaging device, a source follower is provided on-chip for impedance conversion when an output is taken out to an external circuit. The source follower amplifier is obtained by adding an N-type substrate to the lowermost layer in FIG. A P-type region 7 is formed on an N-type silicon substrate, and an N-doped polysilicon gate electrode 9 and an N ⁺ diffusion layer 8 are provided using a film in which a silicon oxide film or a silicon nitride film is sandwiched between silicon oxide films as a gate oxide film. , A driver transistor 16 and a load transistor 17 are formed.

A voltage VDD 10 is applied to the drain of the driver transistor 16, a signal is input to an input terminal 12 connected to the gate electrode 9, and a signal is output from an output terminal 13 connected to the source. The gate and source of the load transistor 17 are connected to the ground 11, and the drain is common to the source of the driver transistor 16, and a signal is output from the output terminal 13. The channel of the load transistor 17 is doped with an N-type impurity to form an N-type region 14.

In a solid-state image pickup device, the diffusion layer portion is generally composed of an N ⁺ diffusion layer, a P-type region, and an N-type substrate from the upper layer due to the vertical overflow drain. Therefore, when a high voltage is applied due to static electricity, for example, the power supply voltage VDD is used to prevent punch-through between the N ⁺ diffusion layer and the N-type substrate.
10 is the voltage required for VDD plus the voltage of alpha (VDD
A protection circuit to which an N-type silicon substrate is added is provided in the lowermost layer of FIG. 4 so that a breakdown occurs when a voltage of about 20 V is applied when 15 V is applied. On the other hand, since the output terminal 13 is also connected to the diffusion layer of the output layer (source of the driver transistor), it is required to provide a protection circuit to prevent punch-through of the output diffusion layer with the substrate due to static electricity or the like. However, since VDD is a constant voltage, a pulse is output to the output layer, so that the capacity of the protection circuit in the output layer becomes the load capacity of the source follower amplifier at the time of actual signal output.

Therefore, in this embodiment, a protection circuit element 3 (for example, a Zener diode) having a required voltage plus an alpha is connected between the output terminal 4 and the ground terminal 5 of the package 1 of the on-chip source follower amplifier. However, the terminals connected to the output terminals 4 should not be in electrical contact with the feet of the package 1 when the package 1 is inserted into the socket. In FIG. 1, both ends of the line of the protection circuit element 3 are formed in a ring shape, the protection circuit element 3 and the ground terminal 5 are connected, and the protection circuit element 3 and the output terminal 4 are insulated. Also, an insulating portion 6 is provided above the output terminal 4 and the wire of the protection circuit element 3 is made elastic so that the output terminal 4 and the terminal of the protection circuit element 3 are usually in electrical contact. , Package 1
Is inserted into the socket, the protection circuit element 3 is pushed, the protection circuit element 3 terminal goes to the insulating portion 6 of the output terminal 4, and the output terminal 4 and the terminal of the protection circuit element 3 are prevented from being in electrical contact. ing. When the package 1 is removed from the socket, the output terminal 4 and the terminal of the protection circuit element 3 make electrical contact again because the wire of the protection circuit element 3 has elasticity.

FIG. 2 shows a second embodiment of the present invention. FIG.
2A is a perspective view when the device is detached from the apparatus, and FIG. 2B is a perspective view when the device is mounted on the apparatus. In FIG. 2, in the case of a solid-state imaging device, it is necessary to take an image, so that consideration is given to inserting the device package 1 into the socket without tilting. The basic principle is the same as that of FIG. 1, but when the device package 1 is inserted into the socket, the protection circuit element 3 is pushed into the groove provided in the package 1, so that the device package 1 is inclined to the socket. Can be inserted without any problem.

In the above embodiments, the NMOS source follower amplifier has been described. However, the present invention can be applied to both PMOS and CMOS as long as the source follower is used. Also,
The load transistor is also buried in FIG. 3 (the threshold voltage is negative and the cut-off is not performed below the threshold voltage), but the surface type (the cut-off is positive and the threshold voltage is below the threshold voltage) Off), the gate is positively biased,
The present invention is applicable even if the load is simply formed by a resistor. Further, the present invention can be applied to a case where a signal is extracted from an on-chip circuit such as an inverter to an external circuit regardless of the source follower.

[0029]

As described above, in the present invention, when a semiconductor device is not mounted, a protection circuit is connected,
By adopting a structure in which a protection circuit is not connected when mounting, it is possible to prevent a load capacitance at the time of device operation and to broaden the band of the on-chip source follower amplifier.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a semiconductor device of the present invention.

FIG. 2 is a diagram showing a second embodiment of the semiconductor device of the present invention.

FIG. 3 is a cross-sectional view illustrating a configuration of a source follower amplifier.

FIG. 4 is a cross-sectional view illustrating a configuration of a protection circuit.

FIG. 5 is a diagram illustrating an example of a conventional semiconductor device.

FIG. 6 is a diagram showing another example of a conventional semiconductor device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Package 2 Semiconductor element 3 Protection circuit element 4 Output terminal 5 Ground terminal 6 Insulation part 7 P-type area 8 N ⁺ diffusion layer 9 Gate electrode 10 VDD 11 Ground 12 Input 13 Output 14 N-type area 15 Gate oxide film 16 Driver transistor 17 Load transistor

Claims (6)

(57) [Claims] 1. A semiconductor device which is electrically connected to the outside by mounting a connection terminal including an output terminal of a semiconductor device, wherein the protection circuit element of the output terminal is mounted when the semiconductor device is not mounted. A semiconductor device which is electrically connected to an output terminal and is not electrically connected to the output terminal when the semiconductor device is mounted. 2. A semiconductor device in which a semiconductor device is packaged and a connection terminal including an output terminal of the package is mounted to make an electrical connection with the outside, wherein a protection circuit element of the output terminal includes an output terminal of the package. Connected between a terminal and a reference potential, and the output terminal and the protection circuit element are electrically connected when the package is not mounted, and are electrically disconnected when the package is mounted. A semiconductor device characterized in that: 3. A protection circuit element is provided between an output terminal of the packaged semiconductor device and a reference potential terminal, and one end of the protection circuit element is electrically connected to the reference potential terminal. The other end of the protection circuit element is electrically connected to the output terminal when the semiconductor device is removed from the socket, and is electrically disconnected from the output terminal when the semiconductor device is inserted into the socket. Semiconductor device. 4. The semiconductor device according to claim 3, wherein the protection circuit element is embedded in a back surface of the package, and a portion of the back surface of the package in which the protection circuit element is embedded is concave. 5. The semiconductor device according to claim 1, wherein an output circuit of said semiconductor device is an on-chip source follower amplifier. 6. The semiconductor device according to claim 1, wherein said semiconductor device is a solid-state image sensor.